JPH0732118B2 - Focusing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focusing device in a reduction projection exposure apparatus used for exposure transfer of a semiconductor or the like.

2. Description of the Related Art Recently, a reduction projection exposure apparatus (hereinafter referred to as a stepper) has been actively used for manufacturing DRAM, LSI, etc. as an apparatus for transferring a pattern drawn on a mask onto a wafer. . A focusing device for clearly projecting a reticle pattern on a wafer through a projection lens is incorporated in this stepper. Examples of this focusing device include, for example, JP-A-60-101540 and the Japan Society for Precision Engineering. , Precision mechanism (Ohm Co., Ltd.), Japan Society for Precision Engineering, Research Meeting No. 89-03, etc. Hereinafter, the focusing device in the conventional stepper will be described with reference to the drawings.

FIG. 7 is a block diagram showing a focusing device in a conventional example.
In FIG. 7, 101 is a wafer, and 102 is a wafer stage for three-dimensionally moving the wafer 101, which is mainly moved in the vertical direction (Z-axis direction) in focusing adjustment. 103
Is a projection lens for projecting and exposing a pattern of a reticle (not shown) on the surface of the wafer 101, 104 is a light emitting element such as an LED,
Reference numeral 105 denotes a lens for converting the light emitted from the light emitting element 104 into parallel rays, and the light emitting element 104 is provided near the focal point of the lens 105. Reference numeral 106 denotes a light-transmitting slit, which is provided with a rectangular slit to allow a part of the parallel light rays to pass therethrough, and is provided such that the center of the rectangular slit is the optical axis. 107 is a lens for focusing the slit light emitted from the light-transmitting slit 106 on the surface of the wafer 101, and 1
08 is a lens for re-imaging the slit light reflected on the wafer 101, 109 is a vibrating mirror that vibrates in the circumferential direction about the optical axis, and 110 is a vibrating frequency f of the vibrating mirror 109.
Mirror driver driven by, 111 is a light-receiving slit having a rectangular slit opened at the center of the optical axis that is conjugate with the vibration center (non-vibration state) of the vibrating mirror 109, and 112 is the image forming point by the lens 108 as well. A light-receiving element provided at a position conjugate with the light-receiving slit 111 for converting light passing through the light-receiving slit 111 into an electric signal. Reference numeral 113 denotes a signal 114 from the light-receiving element 112, which is phase-synchronized with a sine wave signal having a vibration frequency f of the vibration mirror 109. A phase-locked detection processing circuit for detecting and smoothing, 115
Is a wafer stage control drive circuit for calculating the amount of defocus from the signal 116 from the phase synchronous detection processing circuit 113 and moving the wafer stage 102 in the vertical direction (Z-axis direction) accordingly.

The operation of the above configuration will be described below.

In FIG. 7, the reticle, projection lens 103, and wafer 1 are shown.
A state where the reticle pattern is focused on the surface of the wafer 101 by the optical system 01 is shown, and the distance between the projection lens 103 and the wafer 101 at this time is Zo.

The light from the light emitting element 104 is collimated by the lens 105. Of this parallel light, the light near the optical axis passes through the light-sending lift 106, and forms an image of the light-sending slit 106 directly below the center of the projection lens 103 and on the surface of the wafer 101 by the lens 107. This image is reflected on the wafer 101, passes through the lens 108, and is reflected by the vibrating mirror 109 driven by the mirror driver 110 at the vibration frequency f. Since the wafer 101 is placed at the focal point Z = Zo as described above, the reflected light is centered on the center of the slit in the light receiving slit 111 provided in front of the light receiving element 112, that is, the center of the optical axis. Constant amplitude Ao
Vibrates at. Now, the slit width of the light transmitting slit 106 is L ₁ ,
If the slit width of the receiving slit 111 is L ₂ , L ₁ ≤ L ₂ ≤ A
At o, the electric signal 114 of the light receiving element 112 becomes a signal close to a sine wave having a frequency 2f, which is twice the vibration frequency f of the vibrating mirror 109, as indicated by V in FIG. Then, as the wafer stage 102 is moved, the center of the image of the light-sending slit 106 projected on the light-receiving slit 111 moves, so that the waveform changes from I to IX shown in FIG. Light receiving element 11
With respect to the output signal 114 of No. 2, the sine wave signal of the vibration frequency f from the mirror driver 110 is detected as the reference signal by the phase synchronization detection processing circuit 113 and smoothed.
When 01 is at the focal point Z = Zo, the output signal 116 becomes zero. Then, as the wafer stage 102 is moved, an S-shaped characteristic as shown in FIG. 9 is obtained. Wafer stage control drive circuit 115 based on this characteristic,
The position Z of the wafer 101 at the present time is judged by the output signal 116 of the phase-coherent detection processing circuit 113, and the difference (Z
-Zo) moves the wafer stage 102. Focusing is performed in this manner.

Generally, a wafer undergoes various process treatments such as vapor deposition, resist coating, and etching in the process of manufacturing semiconductor elements, and the surface state of the wafer, that is, the reflectance changes with each treatment. Further, even in the same process, the reflectance slightly differs for each wafer. Therefore, in the configuration of the conventional example as described above, even if the distance between the projection lens 103 and the wafer 101 is a constant value, it is determined for each process or the wafer 101.
The amplitude of the output of the light receiving element 112 changes due to the difference in reflectance for each. Therefore, in each of the waveforms in FIG. 8 obtained by changing the distance between the projection lens 103 and the wafer 101, the amplitude also changes according to the change in reflectance. Further, when this signal is subjected to phase synchronous detection processing, the vibrating mirror 109
Even if the frequency and the amplitude are the same, differences such as characteristics A and B occur as shown in FIG. 10 due to the difference in reflectance of the wafer 101. Therefore, it is necessary to move the wafer stage 102 for each wafer 101 and for each process step to obtain the characteristics shown in FIG. 9 and perform focusing according to the characteristics, which requires a lot of time. However, there is a problem that the improvement of the exposure efficiency is hindered.

The present invention is to solve the above problems of the prior art, and normalizes the output of the light receiving element of the focus detection optical system so that the output value after the phase-coherent detection process and the amount of movement of the wafer are The S-shaped characteristic that is the characteristic is a single characteristic that is not related to the reflectance, that is, the normalized characteristic, and
An object of the present invention is to provide a focusing device capable of efficiently performing a focusing operation in a short time without re-taking the characteristics for each process stage.

Means for Solving the Problems Technical means of the present invention for achieving the above object are
Focus detection optical system that forms the light emitted from the light-emitting element on the wafer through the light-sending slit and forms the reflected light on the light-receiving element through the light-receiving slit by the vibrating mirror. Provided in the optical path between the point and the vibrating mirror,
A half mirror that guides one of the focus detection light, which is reflected or transmitted, to the vibrating mirror, and transmission of the half mirror,
Alternatively, a monitor light receiving element for receiving the reflected monitor detection light, a dividing means for obtaining a ratio between the output of the focus detection light light receiving element and the output of the monitor light receiving element, and the vibration frequency of the vibrating mirror are It is provided with means for performing focus detection by performing phase-synchronous detection of the value of the dividing means as a reference signal.

In addition, when the light emitted from the light emitting element is passed through the light-sending slit to form an image on the wafer, the reflected light is reflected by the vibrating half mirror, passes through the light receiving slit as focus detection light, and forms an image on the light receiving element. A division for obtaining the ratio between the output of the focus detection optical system, the monitor detection light receiving element for receiving the monitor detection light transmitted through the vibrating half mirror, and the output of the focus detection light receiving element and the monitor light receiving element. And means for performing focus detection by phase-coherently detecting the value of the dividing means using the vibration frequency of the vibrating mirror as a reference signal.

Further, a focus detection optical system in which light emitted from the light emitting element is passed through the light sending slit to form an image on the wafer, and the reflected light is passed through the light receiving slit by the vibrating mirror to form an image on the light receiving element.
A peak hold circuit for holding the maximum value of the reflected light by the vibrating mirror through the light receiving element and outputting it, a dividing means for obtaining a ratio between the output of the light receiving element and the output of the peak hold circuit, and the vibration. And means for performing focus detection by phase-coherently detecting the value of the dividing means using the vibration frequency of the mirror as a reference signal.

Therefore, according to the present invention, the output of the light receiving element of the focus detection optical system of the wafer and the monitor detection light reflected or transmitted by the half mirror on the reflection side from the wafer in the focus detection optical system are received. The ratio with the light receiving element for monitoring is obtained by dividing means, or the output of the light receiving element of the focus detection optical system of the wafer and the transmitted light of the vibration half mirror on the reflection side from the wafer in this focus detection optical system are received. Vibratory mirror on the reflection side from the wafer obtained by dividing the ratio with the output of the monitor light receiving element by dividing means, or the output of the light receiving element of the focus detection optical system of the wafer and the output of this light receiving element by the peak hold circuit The ratio to the maximum value of the reflected light is calculated by dividing means, the output of the light receiving element of the focus detection optical system is normalized, and the frequency of the vibrating mirror or the vibrating half mirror is referenced. By performing phase-synchronous detection of the above-mentioned normalized value as a signal for focus detection, focus detection can be performed without depending on changes in the reflectance of the wafer.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

First, a first embodiment of the present invention will be described.

FIG. 1 is a block diagram showing a focusing device according to the first embodiment of the present invention.

FIG. 1 shows the state when the wafer is in focus.

In FIG. 1, reference numeral 1 is a wafer, and 2 is a wafer stage for moving the wafer 1 three-dimensionally. In focusing operation, the wafer stage is mainly moved in the vertical direction (Z-axis direction). 3 is a projection lens for projecting and exposing a pattern of a reticle (not shown) on the surface of the wafer 1, and 4 is a LE in the focus detection optical system.
A light emitting element 5 such as D is a lens for making point-like light emitted from the light emitting element 4 into parallel rays, and the light emitting element 4 is provided near the focal point of the lens 5. Reference numeral 6 denotes a light-sending slit, which is provided with a rectangular slit for passing a part of the parallel rays from the lens 5, and is provided so that the center of the rectangular slit serves as the optical axis. Reference numeral 7 denotes a lens, and when the exposure is in focus, the light passing through the light-sending slit 6 is used for the wafer 1 immediately below the center of the projection lens 3.
Is provided at a position where an image is formed on the surface P of. Reference numeral 8 is a lens for forming an image of the slit image reflected on the wafer 1 again, and 9 is a half mirror, which reflects a part of the light passing through the lens 8 and transmits the remaining part. Reference numeral 10 denotes a monitor light receiving element that receives the monitor detection light reflected by the half mirror 9, and is located on the optical axis of the reflected monitor detection light and at a position conjugate to the half mirror 9 with the image forming point of the lens 8. It is provided. Reference numeral 11 is a vibrating mirror that vibrates in the circumferential direction around the optical axis and reflects the focus detection light that has passed through the half mirror 9, and 12 is a driver that vibrates the vibrating mirror 11 at a frequency f and a constant amplitude. It has a built-in oscillator circuit of f. Reference numeral 13 denotes a light-receiving slit, which has an optical axis which is conjugate with the vibration mirror 11 when the vibration mirror 11 is at the vibration center, that is, when the vibration is stopped. Reference numeral 14 denotes a light receiving element for converting the light passing through the light receiving slit 13 into an electric signal, which is provided near the position of the oscillating mirror 11 which is in a stopped state and conjugate with the focal point of the lens 8. Reference numeral 15 is an amplifier that amplifies an electric signal of the light receiving element 14 of the focus detection optical system. Reference numeral 16 denotes an amplifier, which amplifies an electric signal of the monitor light receiving element 10. 17 is a divider for dividing the output of the amplifier 15 by the output of the amplifier 16, and 18 is a driver 12
Of the divider 17 as a reference signal, the phase-locking detector detects the output of the divider 17 by phase-locking, 19 is a low-pass filter for smoothing the output signal of the phase-locking detector 18, and 20 is wafer stage control. This is a circuit, and the amount of movement of the wafer stage 2 to the focal point is determined by the output signal of the low-pass filter 19 based on the phase-coherent detection characteristic obtained by changing the distance between the projection lens 3 and the wafer 1. Determine and output a movement signal. Reference numeral 21 denotes a wafer stage drive circuit, which is a drive circuit for moving the wafer stage 2 based on the movement signal output from the wafer stage control circuit 20.

The operation of the above configuration will be described below.

The light emitted from the light emitting element 4 of the focus detection optical system is reflected by the lens 5
It becomes a parallel light. Of the parallel light, the light in the vicinity of the optical axis passes through the light-sending slit 6 and forms an image of the light-sending slit 6 at a point P directly below the center of the projection lens 3 by the lens 7 and on the surface of the wafer 1. . This slit image is reflected on the wafer 1 and reaches the lens 8. The lens 8 is for forming an image, and the light passing through the lens 8 is divided by the half mirror 9 into reflected light (monitor detection light) and transmitted light (focus detection light). The reflected light is reflected by the lens 8 against the half mirror 9.
It reaches the monitor light-receiving element 10 provided at the point conjugate with the focal point of, that is, at the image forming point of the reflected light, and is converted into an electric signal by this monitor light-receiving element 10. In the focusing operation, several tens of μm to several hundreds in the vertical direction (Z-axis direction) with reference to the focal point Z = Zo.
It moves slightly by about μm, and in such a case, the output of the monitor light-receiving element 10 can be regarded as a constant value as long as the reflectance of the wafer 1 does not change. On the other hand, the light transmitted through the half mirror 9 tries to form an image at the focal point of the lens 8 shown by the dotted line in FIG.
Is reflected by an oscillating mirror 11 driven at a frequency f and a constant amplitude, and an image is formed at a point conjugate with the oscillating mirror 11. A light receiving element 14 is provided at this conjugate point, and a light receiving slit 13 is provided immediately before the light receiving element 14. Since the wafer 1 is placed at the focal point Z = Zo as described above, the light reflected by the vibrating mirror 11 has a constant amplitude with the center of the slit in the light receiving slit 13, that is, the optical axis as the center. Vibrating. This constant amplitude
Ao. The light passing through the light-receiving slit 13 receives the light-receiving element 14
The light is received by, and the output signal of the light receiving element 14 is amplified by the amplifier 15. The output of the monitor light receiving element 10 is amplified by the amplifier 16.

Now, when the vibrating mirror 11 is stopped at the center of vibration, the ratio of the output of the light receiving element 12 of the focus detection optical system and the output of the monitor light receiving element 16 is constant, and the reflected light of the half mirror 9 and the transmitted light are transmitted. It is the ratio of light quantity to light. Therefore, the output of the divider 17 is 1 by adjusting the amplifiers 15 and 16 so that the ratio becomes 1. Therefore, when the vibrating mirror 11 is stopped, whether the wafer stage 2 is moved in the horizontal direction (X, Y axis direction) or in the vertical direction (Z axis direction), the reflectance is Divider 17 even if it is replaced with a different wafer 1
Output is 1. Next, the Z-axis of the wafer stage 2 is moved to the focal point (this point is Zo), and the vibrating mirror is again used.
When 11 is actuated, the image of the light-sending slit 6 has a width on the surface of the light-receiving slit 13 with the center of the slit as the center.
It vibrates with Ao. When the slit gaps of the light-transmitting slit 6 and the light-receiving slit 13 are L ₁ and L ₂ , respectively, when L ₁ ≤L ₂ ≤Ao,
The output of the divider 17 is a normalized analog waveform having a maximum value of 1 and a frequency of 2f, as indicated by V in FIG.
Then, by moving the Z axis of the wafer stage 2, it is possible to obtain a normalized waveform such as I to IX in FIG. Also, even if the reflectance differs for each wafer 1,
Further, even if the reflectance is partially different on the same wafer 1, or the reflectance is different at each process stage,
Divider obtained when the wafer 1 is moved in the Z-axis direction
The output signal of 17 has the normalized waveforms shown in FIGS. Therefore, the output of the divider 17 is used as the signal input of the phase-locking detector 18, the frequency signal of the driver 12 is phase-locked as the reference signal, and its output is smoothed by the low-pass filter 19, and its output is According to the amount of movement of the wafer 1 in the Z-axis direction, an S-shaped characteristic whose maximum value becomes a constant value Vo is obtained as shown in FIG. This characteristic is always the same even if the reflectance at the point P on the wafer 1 is different.

Therefore, the S-shaped characteristic shown in FIG. 3 is stored in the wafer stage control circuit 20, and the output of the low-pass filter 19 when the wafer 1 is not in focus is set to the wafer stage control circuit 20.
To the wafer stage drive circuit 21 to calculate the amount of movement of the wafer stage 2 to the in-focus point by comparing the input signal with the S-shaped characteristic.
The wafer 1 can be moved to the focal point by driving the wafer stage 2 or comparing with the S-shaped characteristic and driving the wafer stage 2 until the output of the low pass filter 19 becomes zero.

As described above, according to the present embodiment, the light emitted from the light emitting element 4 is passed through the light-sending slit 6, is imaged by the lens 7, is reflected by the wafer 1, and the reflected light is imaged again by the lens 8. However, before forming an image, the half mirror 9 separates the reflected light and the transmitted light, and the reflected light is detected by the monitor light-receiving element 10.
The transmitted light is reflected by the vibrating mirror 11, and the reflected light is slit.
The light is passed through 13 and detected by the light receiving element 14. Then, the light receiving element 14
The amplified output of the
The output after amplification is normalized by dividing it by a divider 17, and the normalized value is obtained by using the vibration frequency signal of the vibration mirror 8 as a reference.
18 and the low-pass filter 19 detect and smooth, and the wafer stage control circuit 20 obtains the moving distance of the wafer 1 to the in-focus point.
By moving and focusing the wafer stage 2 by the wafer stage vibrating circuit 21, it is not necessary to re-obtain the S-shaped characteristic even if the reflectance of the wafer 1 is different, and to immediately respond to the change of the reflectance of the wafer 1. It is possible to provide an efficient focusing device capable of performing the above.

In this embodiment, the case where the slit is not provided immediately before the monitor light receiving element 10 has been described, but a slit similar to the light receiving element 14 may be provided. Although the reflected light of the half mirror 9 is the monitor detection light and the transmitted light is the focus detection light, the transmitted light may be the monitor detection light and the reflected light may be the focus detection light.

Next, a second embodiment of the present invention will be described.

FIG. 4 is a block diagram showing a focusing device according to the second embodiment of the present invention. Note that FIG. 4 shows a state in which the wafer is in focus.

In the present embodiment, the same components as those in the first embodiment are designated by the same reference numerals, the description thereof will be omitted, and a different configuration will be described.

The feature of this embodiment is that, as shown in FIG.
In place of the two members of the half mirror 9 and the vibrating mirror 11 in the first embodiment, a half mirror is a vibrating mirror.
22 is provided, and the light receiving element 10 for monitoring is provided at the image forming point of the transmitted light of the vibrating half mirror 22. Since the vibrating half mirror 22 vibrates in the circumferential direction, the optical axis and focus of the transmitted light also move in accordance with the vibration. for that reason,
The monitor light-receiving element 10 should cover the light reception with respect to the movement of the image forming point, that is, the focal point when the vibration half mirror 22 is positioned in a direction perpendicular to the optical axis in the vibration stopped state and is vibrating. Set to a size that allows With such a configuration, when there is no change in the reflectance at the point P, the received light amount of the transmitted light is always a constant value even if the vibrating half mirror 22 is vibrating, and the monitor light receiving element 10 functions as a monitor. Can be fulfilled

The operation of the above configuration will be described below.

Regarding the operation from the light receiving element 4 to the lens 8, the first
Since it is the same as the embodiment described above, the description thereof will be omitted. The light passing through the lens 8 is separated by the vibrating half mirror 22 into reflected light and transmitted light. The reflected light is the same as in the first embodiment, and the transmitted light tries to form the image of the light-sending slit 6 at the focal point of the lens 8, but the vibrating half mirror 22 vibrates. The imaging point also moves in the circumferential direction. However, this amount of movement is several times the slit width of the light-sending slit 6 and is not large, and the monitor light-receiving element 10 has a light-receiving area that can sufficiently cover this movement, so even if it vibrates. It always receives a fixed amount of light. Therefore, the monitor light receiving element 10 operates in the same manner as the monitor light receiving element 10 in the first embodiment. Therefore, when the vibration half mirror 22 is stopped at the vibration center, the light receiving element 14
The ratio of the output of the light receiving element 10 to the output of the monitor light receiving element 10 is the light amount ratio of the reflected light of the vibrating half mirror 22 and the transmitted light. The amplifiers 15 and 16 are adjusted so that the ratio becomes 1, and the amplifier 16
The output of is the divider input of divider 17, the output of amplifier 15 is the divider
When the division target of 17 is input, the output of the divider 17 becomes 1 as in the first embodiment. Next, as in the first embodiment, when L ₁ ≤L ₂ ≤Ao, the oscillating half mirror 22 is operated and the wafer stage 2 is moved in the Z-axis direction, the output of the divider 17 becomes the second value. Generate a normalized signal as I to IX in the figure. Even if the reflectance at the point P is different, the same normalized signal as shown in FIG. 2 can be obtained.
As a result, this signal is converted into a phase-locked detector 18 and a low-pass filter 19
The characteristics detected and smoothed by are as shown in FIG.
Therefore, using this characteristic, the focusing operation can be performed as in the first embodiment.

As described above, according to this embodiment, the light emitted from the light emitting element 4 is collimated by the lens 5, and the collimated light is collimated by the light transmitting slit 6.
An image is formed in the vicinity of the wafer 1 by the lens 7, the image is reflected at the point P, and the reflected light is imaged again by the lens 8. The light from the lens 8 is divided into reflected light and transmitted light by the vibrating half mirror 22, the reflected light is passed through the light receiving slit 13 and received by the light receiving element 14, while the transmitted light is received by the monitor light receiving element 10. The amplified output of the monitor light-receiving element 10 is divided by the divider 17, and the amplified output of the light-receiving element 14 is divided by the divider 17 as a divided input for normalization.
Using the oscillation frequency signal of as a reference, the normalized value is detected and smoothed by the phase-locking detector 18 and the low-pass filter 19, and the moving distance of the wafer 1 to the focal point is obtained by the wafer stage control circuit 20. Even if the wafer stage driving circuit 21 moves and focuses the wafer stage 2 so that the reflectance of the wafer 1 is different, it is not necessary to retake the S-shaped characteristic each time the reflectance is changed, and the reflectance of the wafer 1 is changed. It is possible to provide an efficient focusing device capable of immediately responding to.

In this embodiment, a light-receiving slit may be provided just before the monitor light-receiving element 10 like the light-receiving element 14.

Next, a third embodiment of the present invention will be described.

FIG. 5 is a block diagram showing a focusing device according to the third embodiment of the present invention. Note that FIG. 5 shows a state in which the wafer is in focus.

In the present embodiment, the same components as those of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted, and different configurations will be described.

The feature of this embodiment is that, as shown in FIG.
A peak hold circuit 23 is used in place of the half mirror 9, the monitor light receiving element 10 and the amplifier 16 in the first embodiment.
There is a point. This peak hold circuit 23 is an amplifier
It has the function of finding the peak value (maximum value) from the 15 output signals and storing the value, and the function of holding and outputting the stored value and updating the held value at regular intervals.

The operation of the above configuration will be described below.

Regarding the operation from the light emitting element 4 to the lens 8, the first
Since it is the same as the embodiment described above, the description thereof will be omitted. The light passing through the lens 8 is reflected by the vibrating mirror 11,
11, the light-sending slit 6 is at a point conjugate with the focal point of the lens 8.
Form an image of. A light receiving element 14 is provided at this image forming point, and a light receiving slit 13 is provided immediately before the light receiving element 14. Then, the imaging light reflected by the vibrating mirror 11 passes through the light receiving slit 13 and reaches the light receiving element 14. Now, the slit intervals of the light sending slit 6 and the light receiving slit 13 are respectively set.
Consider L ₁ and L ₂ and the amplitude of the vibration mirror 11 on the light receiving slit 13 is Ao, and consider a case where the wafer 1 is at the focal point (Z = Zo). On the surface of the light receiving slit 13, the image of the light transmitting slit 6 vibrates with the amplitude Ao, but since the wafer 1 is in focus, the vibration center is the rectangular slit center of the light receiving slit 13. Therefore, L ₁ ≤ L ₂ , Then, the relationship shown in FIG. 6 (a) is obtained, and the correlation between the output of the light receiving element 14 provided immediately after the light receiving slit 13 and the vibration frequency f of the vibrating mirror 11 is well understood (6th).
See FIG. (B)). Here, assuming that the peak value (maximum value) of the output of the light receiving element 14 is Bo, the output becomes Bo because the slit image of the light transmitting slit 6 does not protrude into the gap of the light receiving slit 13. That is the case. Since the center of vibration is now at the slit center of the light receiving slit 13, the light receiving element
The maximum output of 14 is just when the vibration is stopped, but when the wafer 1 is out of focus, the vibration center moves laterally as shown in FIG. 6 (c). To do. Then, when the movement amount of the vibration center is taken with the slit center of the light receiving slit 13 as a reference and the value is M, the light transmitting slit 6 always enters the light receiving slit 13 when M ≦ Ao. The peak value Bo appears in the output of 14 (see FIG. 6 (d)). On the other hand, in the S-shaped characteristic as shown in FIG. 9, the portion generally used for the focusing operation is a linear portion including the zero point, and within this range, the movement amount M of the vibration center is M ≦ Ao. Become. As a result, a peak value always appears in one cycle of vibration. Further, in FIG.
This peak value Bo will be a constant value if the reflectance is unnecessary, but the peak value Bo will change accordingly if the reflectance changes. Therefore, as shown in FIG. 5, if the output signal of the light receiving element 14 is amplified by the amplifier 15 and its peak value is B, the peak hold circuit 23 captures this peak value B and stores the value, and Hold and output. Then, this value can be updated at regular intervals. The holding output B of the peak hold circuit 23 is used as the division input of the divider 17,
When the output of the amplifier 15 is used as the divided input of the divider 17, the output of the divider 17 becomes a normalized signal as shown in FIG. 2 as in the first embodiment. The output of the divider 17 does not depend on the reflectance of the wafer 1 and is shown in FIG.
It becomes a signal with a waveform like IX. As a result, the characteristics obtained by detecting and smoothing this signal by the phase lock detector 18 and the low-pass filter 19 are as shown in FIG. Therefore, using this characteristic, the focusing operation can be performed as in the first embodiment.

As described above, according to this embodiment, the light emitted from the emitting element 4 is collimated by the lens 5, the collimated light is passed through the light-sending slit 6, and the lens 7 forms an image in the vicinity of the wafer 1. Is reflected at a point P, and the reflected light is imaged again by the lens 8. The light from the lens 8 is reflected by the vibrating mirror 11, passes through the light receiving slit 13, and is received by the light receiving element 14. This light receiving element
The output of 14 is amplified by the amplifier 15, and this output is used as the divided input of the divider 17. At the same time, the output of the amplifier 15 is input to the peak hold circuit 23, the peak value of the light receiving element 14 is detected, stored and output, and this output is used as the division input of the divider 17. As a result, the output of the divider 17 becomes a normalized value. Using the vibration frequency signal of the vibrating mirror 11 as a reference, the normalized signal is detected and smoothed by the phase-locking detector 18 and the low-pass filter 19, and the wafer stage control circuit 20 moves the wafer 1 to the focal point. By obtaining the distance and moving the wafer stage 2 by the wafer stage drive circuit 21 to bring it into focus, it is necessary to re-acquire the S-shaped characteristics as shown in FIG. 9 every time the reflectance of the wafer 1 changes. Therefore, it is possible to immediately deal with a change in the reflectance of the wafer 1, and an efficient focusing device can be provided.

EFFECTS OF THE INVENTION As described above, according to the present invention, the output of the light receiving element of the focus detection optical system of the wafer and the monitor that is reflected or transmitted by the half mirror on the reflection side from the wafer in the focus detection optical system. The ratio of the detection light received to the monitor light receiving element is obtained by the dividing means, or the output of the light receiving element of the focus detection optical system of the wafer and the vibration half mirror of the reflection side from the wafer in the focus detection optical system. The ratio from the output of the monitor light receiving element that received the transmitted light is obtained by dividing means, or the output of the light receiving element of the focus detection optical system of the wafer and the output of this light receiving element are obtained from the peak hold circuit from the wafer. The ratio of the maximum value of the light reflected by the oscillating mirror on the reflection side is calculated by dividing means, the output of the light receiving element of the focus detection optical system is normalized, and the frequency of the oscillating mirror or the oscillating half mirror is reset. As a reference signal, the normalized value is phase-synchronized to detect focus. Therefore, the focusing operation can be performed quickly and efficiently without depending on the change in the reflectance of the wafer.

[Brief description of drawings]

FIG. 1 is a block diagram showing a focusing device in a first embodiment of the present invention, FIG. 2 is a waveform diagram showing an output signal of a division circuit in the focusing device in the first embodiment, and FIG. Is the first
4 is a characteristic diagram showing the relationship between the output of the low-pass filter circuit in the focusing device and the amount of movement of the wafer in the Z-axis direction in FIG. 4, and FIG. 4 shows the focusing device in the second embodiment of the present invention. Diagram,
FIG. 5 is a block diagram showing a focusing device in a third embodiment of the present invention, FIG. 6 is a correlation diagram showing a positional relationship of slit images in the focusing device in the third embodiment, and FIG. FIG. 8 is a configuration diagram showing a conventional focusing device, FIG. 8 is a waveform diagram showing an output signal of a light receiving element in the conventional focusing device, and FIGS. 9 and 10 are diagrams showing the conventional focusing device. It is a characteristic view which shows the relationship between the output of a phase synchronous detection processing circuit and the amount of movement of the wafer in the Z direction. 1 ... Wafer, 2 ... Wafer stage, 3 ... Projection lens, 4 ... Issuing element, 5 ... Lens, 6 ... Light transmitting slit, 7, 8 ... Lens, 9 ... Half mirror, 10 ... … Monitor light-receiving element, 11 …… Vibration mirror, 12 …… Driver,
13 ... Receiving slit, 14 ... Receiving element, 15, 16 ... Amplifier, 17 ... Divider, 18 ... Phase-locked detector, 19 ... Low-pass filter, 20 ... Wafer stage control circuit, 21 …… Wafer stage drive circuit, 22 …… Vibration half mirror, 23 …… Peak hold circuit.

Claims (3)

[Claims] 1. A focus detection optical system in which light emitted from a light-emitting element is passed through a light-sending slit to form an image on a wafer, and the reflected light is passed through a light-receiving slit by an oscillating mirror to be imaged on a light-receiving element. A half mirror that is provided in the optical path between the incident / reflecting point of the wafer and the vibrating mirror and guides one of focus detection light that is either reflected or transmitted to the vibrating mirror, and monitor detection that is transmitted or reflected by the half mirror. A light-receiving element for monitoring that receives light, a division means for obtaining a ratio of the output of the light-receiving element of the focus detection light and the output of the light-receiving element for monitoring, and the division using the vibration frequency of the vibrating mirror as a reference signal. A focusing device comprising means for performing focus detection by phase-coherently detecting the value of the means. 2. Light emitted from a light emitting element is passed through a light emitting slit to form an image on a wafer, and the reflected light is reflected by a vibrating half mirror and passed through a light receiving slit as focus detection light to be imaged on a light receiving element. The focus detection optical system, the monitor detection light receiving element that receives the monitor detection light transmitted through the vibration half mirror, and the ratio of the output of the focus detection light receiving element to the output of the monitor light receiving element. A focusing device comprising: a dividing unit for obtaining a value; and a unit for performing focusing detection by phase-synchronously detecting the value of the dividing unit using the vibration frequency of the vibrating mirror as a reference signal. 3. A focus detection optical system in which light emitted from a light-emitting element is passed through a light-sending slit to form an image on a wafer, and the reflected light is passed through a light-receiving slit by an oscillating mirror to form an image on the light-receiving element. A peak hold circuit for holding the maximum value of the reflected light by the vibrating mirror through the light receiving element and outputting it, a dividing means for obtaining a ratio between the output of the light receiving element and the output of the peak hold circuit, and the vibration. A focusing device provided with means for performing focus detection by phase-synchronously detecting the value of the dividing means using the vibration frequency of the mirror as a reference signal.